1. Field of the Invention
The present invention relates to an image processing performed to enhance a quality of an image in a document scanned and input by an image input device, and more particularly, to a digital image quality enhancing method and apparatus designed to enhance a quality of digital image on a background region of a document, in which degradation of an image quality occurs.
2. Description of the Related Art
FIG. 1 is a flowchart showing a conventional image processing method to enhance a digital image quality disclosed in Korean Patent Publication No. 1999-43374. When reading a document image using an image input device including a memory for white shading correction, a memory for black shading correction, and a preprocessor with a maximum value detector, the conventional image quality enhancement method generates reference data to correct a distortion of the document image and sets maximum and minimum reference voltages in order to adjust a contrast and a brightness of the document image and to eliminate a background color. The method further compensates for image distortion by simultaneously performing the black shading correction and the white shading correction on the document image using the reference data and by performing image processing on the document image using the set maximum and minimum reference voltages. The method outputs the document image subjected to image distortion correction and image processing as digital image data. In the image input device such as a scanner, the black shading correction is performed to compensate for a difference between pixels due to different characteristics of an image sensor such as a charge coupled device (CCD) or a contact image sensor (CIS). Along with the black shading correction, the white shading correction is performed to correct the distortion caused by non-uniformity in a light source, to correct local variations in reflectivity of a mirror and transmissivity of a lens in a scanner optical system, to correct a contamination on a light path, etc. According to the conventional image processing method, the contrast is corrected based on only the data obtained by the white shading correction and the black shading correction. However, varying a background intensity of the document image cannot be reflected only with the above shading corrections, which makes the conventional image processing method not adaptive to a document. Another problem is that a longer processing time is required for an image quality enhancement because a prescan is necessary to obtain maximum brightness data for brightness correction.